Position encoder

ABSTRACT

An optical encoder that includes an optical grating and a quadrature optical encoder sensor that move relative to each other. The optical grating includes a first encoder bar and a plurality of second encoder bars, wherein the first encoder bar is optically configured to change an amplitude of an output of the quadrature optical encoder sensor.

BACKGROUND OF THE DISCLOSURE

[0001] Printing systems such as ink jet printers and electrophotographicprinters can employ position encoders to track the position of movingcomponents such as print drums and printheads. Position encoderscommonly include an optical grating and an optical encoder sensor thatmove relative to each other pursuant to movement of the component whoseposition is being tracked. It can be useful to determine a reference orhome position for the component whose position is being tracked, and itcan be difficult to determine such reference or home position.

BRIEF DESCRIPTION OF DRAWINGS

[0002]FIG. 1 is a schematic block diagram of an embodiment of a printingapparatus.

[0003]FIG. 2 is a schematic block diagram of an embodiment of a markingapparatus that can be used in the printing apparatus of FIG. 1.

[0004]FIG. 3 is a schematic illustration of an embodiment of a linearoptical grating.

[0005]FIG. 4 is a schematic illustration of an embodiment of anotherlinear optical grating.

[0006]FIG. 5 is a schematic illustration of an embodiment of a furtherlinear optical grating.

[0007]FIG. 6 sets forth schematic quadrature waveforms that would beproduced as the linear optical track of FIG. 3, FIG. 4 or FIG. 5 movesbetween the emitter and the detectors of the quadrature optical encodersensor of FIG. 2.

[0008]FIG. 7 is a schematic illustration of an embodiment of a circularoptical grating.

[0009]FIG. 8 is a schematic illustration of an embodiment of anothercircular optical grating.

[0010]FIG. 9 is a schematic illustration of an embodiment of yet anothercircular optical grating.

[0011]FIG. 10 is a schematic illustration of a further circular opticalgrating.

DETAILED DESCRIPTION OF THE DISCLOSURE

[0012]FIG. 1 is a schematic block diagram of an embodiment of a printingapparatus that includes a print drum 11 that is driven by a gear train13, for example. A marking system 20 applies marking material to theprint drum 11 to form an image that is transferred to a print outputmedium 15. The marking system 20 can be an ink jet marking system or anelectrophotographic marking system, for example.

[0013] An optical encoder system comprised of an optical encoder grating17 and a quadrature optical encoder sensor 19 that move relative to eachother pursuant to movement of the print drum 11 provide position relatedinformation that can be processed by a printer controller 10, forexample, to determine angular position of the print drum 11. By way ofillustrative example, the optical encoder sensor 19 can be mechanicallycoupled to the print drum 11 or the gear train 13, or the opticalencoder grating 17 can be mechanically coupled to the print drum 11 orthe gear train 13. The optical encoder grating 17 includes an opticaltrack that is encoded to identify a predetermined position of the printdrum 11. The optical track can generally comprise a series ofalternating light and dark regions or areas, wherein the light areas canbe reflective or transmissive. In a transmissive system, the light areaswould be transmissive while the dark areas would be less transmissivethan the light areas. In a reflective system, the light areas would bereflective while the dark areas would be less reflective that the lightareas.

[0014] For convenience, since the optical tracks disclosed herein caninclude areas of relative lightness or darkness, when an area isdescribed as being lighter than another area, the lighter area isconfigured to be more transmissive in a transmissive system or morereflective in a reflective system. Similarly, when an area is describedas being darker than another area, the darker area is configured to beless transmissive in a transmissive system or less reflective in areflective system. Light areas can also be called spaces, slots orwindows since they separate dark areas. Dark areas can be convenientlycalled encoder bars.

[0015] By way of illustrative example, the quadrature optical encodersensor 19 can include a light source or emitter such as an LED and aplurality of photodetectors such as photodiodes for detecting thepattern of light transmitted or reflected by the optical track of theoptical encoder grating as it moves through a sense region. The opticalencoder sensor 19 can be implemented by an Agilent HEDS-9202 opticalincremental encoder module that is available from Agilent Technologies,Inc. The optical track of the optical grating 17 modulates the lightprovided by the light source, and the quadrature optical encoder sensor19 senses the light and dark areas of the optical track by detecting themodulated light provided by the optical track. The output of thequadrature optical encoder sensor 19 can comprise quadrature waveformsthat can be provided to the controller 10 to control the operation ofthe gear train 13.

[0016]FIG. 2 is a schematic block diagram of an embodiment of a markingsystem that includes an ink jet printhead 31 that deposits drops 33 ofink on an intermediate transfer surface 35 that is disposed on the printdrum 11. The ink drops 33 can be melted solid ink that is provided by asupply 37 of solid ink. The intermediate transfer surface 35 comprisesfor example a liquid layer that is applied to the print drum 11 by anapplicator assembly 39 that can include an oil impregnated roller and ametering wiper or blade, for example as shown in commonly assigned U.S.Pat. No. 6,431,703. A linear optical encoder grating 117 and aquadrature optical encoder sensor 119 can be provided to detect theposition of the printhead 31. The linear optical encoder grating 117 canmove with movement of the printhead 31, or the quadrature opticalencoder sensor can move with movement of the printhead 31.

[0017]FIGS. 3, 4 and 5 schematically illustrate embodiments of anoptical encoder grating that includes a linear optical track 51 disposedon a linearly translatable strip 53. The optical track includes darkareas or bars 55, 61, 62, 63, 64, 65 that can be uniformly linearlyspaced center to center C so as to have a constant pitch. The dark areas61-65 are contiguously adjacent, and dark areas 55 can be on one or bothsides of the dark areas 61-65. The dark areas 55, 61-65 can berectangular, each having a width WA, W1-W5 and a height HA, H1-H5. Theside edges of the dark areas can be linear, or they can be non-linear asschematically illustrated in FIG. 8 for a circular optical track.

[0018] Each of the dark areas 55, 61-65 can be black, a non-black shadeof gray, or patterned, for example. Suitable patterns can include linesegments, dots, or rectangles.

[0019] The contiguously adjacent dark areas 61-65 are more particularlyoptically different from the dark areas 55 which can be opticallysubstantially identical, such that the quadrature output waveforms ofthe quadrature sensor 119 change in amplitude when the dark areas 61-65are sensed by the quadrature sensor 119. In other words, the dark areas61-65 are configured to modulate the light sensed by the quadraturesensor 119 (FIG. 2) so that the quadrature waveforms change inamplitude. Such change can be detected to indicate a particular linearposition of the optical grating 117 (FIG. 2) and thus a particularlinear position of the printhead 31 (FIG. 2), for example.Alternatively, a single optically different dark area can be employedinstead of a plurality of contiguously adjacent optically different darkareas 61-65, for example wherein the dark area 63 is the sole dark areathat is optically different from the dark areas 55, 61-62 and 64-65.

[0020] For example, as schematically depicted in FIG. 3, the dark areas61-65 can be narrower than the dark areas 55 which can be ofsubstantially identical width. Alternatively, the dark areas 61-65 canbe wider than the dark areas 55 which can be of substantially identicalwidth. In these implementations the heights HA, H1-H5 of the dark areas55, 61-65 can be substantially the same.

[0021] As another example, as schematically depicted in FIG. 4, the darkareas 61-65 can be shorter than the dark areas 55, wherein the darkareas 55, 61-65 can be of substantially the same width, and wherein theheights of the dark areas 61-65 are less than the height of the field ofview of the quadrature optical encoder sensor 119. That is, the heightsof the dark areas 55, 61-65 are configured such that the quadratureoptical encoder can see the differences in height. As yet anotherexample, the heights of the dark areas 61-65 can be greater than theheights of the dark areas 55 which can be of substantially identicalheight.

[0022] As yet another example, as schematically depicted in FIG. 5, thedark areas 61-65 can be of lighter shades of gray than the dark areas 55which can be of substantially the same shade of gray, such that the darkareas 61-65 have greater reflectance in a reflective system or greatertransmissivity in a transmissive system. Alternatively, the dark areas61-65 can be of darker shades of gray than the dark areas 55 so as tohave less reflectance in a reflective system or less transmissivity in atransmissive system. Also, dark areas 61-65 can have a different patternor patterns than the dark areas 55, such that the dark areas 61-65 canhave a greater reflectance (in a reflective system) or transmissivity(in a transmissive system) than the dark areas 55, or less reflectance(in a reflective system) or transmissivity (in a transmissive system)than the dark areas 55. In these implementations, the heights HA, H1-H5can be substantially the same and/or the widths WA, W1-W5 can besubstantially the same.

[0023]FIG. 6 sets forth schematic quadrature waveforms that would beproduced as the optical track of FIG. 3, FIG. 4 or FIG. 5 moves betweenthe emitter and the detectors of the quadrature optical encoder sensor119.

[0024] The foregoing concepts regarding the optical characteristics ofencoder bars can be implemented in an encoder wheel or disc, for exampleas schematically illustrated in FIGS. 7, 8, 9 and 10. An encoder wheelor disc can be employed for example to detect the position of arotatable print drum 11 (FIG. 1).

[0025]FIGS. 7, 8, 9 and 10 are schematic illustrations of embodiments ofan optical encoder grating that includes a circular optical track 51disposed on a rotatable disc 53. The optical track 51 includes darkareas or bars 55, 61, 62, 63, 64, 65 disposed about the center of theoptical track 51. The dark areas 55, 61-65 of the track can be uniformlyangularly spaced center to center C so as to have a constant pitch. Thedark areas 61-65 are contiguously adjacent, and dark areas 55 can be onone or both sides of the dark areas 61-65. Each of the dark areas 55,61-65 has an angular width WA, W1-W5 and a radial height HA, H1-H5. Thesides of the dark areas can be linear or they can be non-linear asschematically represented in FIG. 8. By way of specific example, thedark areas 55, 61-65 can comprise truncated circular sections or wedges.

[0026] Each of the dark areas 55, 61-65 can be black, a non-black shadeof gray, or patterned, for example. Suitable patterns can include linesegments, dots, or rectangles.

[0027] The contiguously adjacent dark areas 61-65 are more particularlyoptically different from the dark areas 55 which are opticallysubstantially identical, such that the quadrature output waveforms ofthe quadrature optical encoder sensor 19 (FIG. 1) change in amplitudewhen the dark areas 61-65 are sensed by the quadrature optical encodersensor 19. In other words, the dark areas 61-65 are configured tomodulate the light sensed by the quadrature optical encoder sensor 19 sothat the quadrature waveforms change in amplitude. Such change can bedetected to indicate a particular angular position of the opticalgrating 17 (FIG. 1) and thus a particular angular position of the printdrum 11 (FIG. 1), for example. Alternatively, a single opticallydifferent dark area can be employed instead of a plurality ofcontiguously adjacent optically different dark areas 61-65.

[0028] For example, as schematically depicted in FIGS. 7 and 8, the darkareas 61-65 can be narrower than the dark areas 55 which can be ofsubstantially identical width. Alternatively, the dark areas 61-65 canbe wider than the dark areas 55 which can be of substantially identicalwidth or thickness.

[0029] As another example, as schematically depicted in FIG. 9, the darkareas 61-65 can be shorter than the dark areas 55, wherein the darkareas 55, 61-65 can be of substantially the same angular width, andwherein the radial heights of the dark areas 61-65 are less than theradial height of the field of view of the quadrature optical encodersensor 119. That is, the radial heights of the dark areas 55, 61-65 areconfigured such that the quadrature optical encoder can see thedifferences in radial height. As yet another example, the radial heightsof the dark areas 61-65 can be greater than the radial heights of thedark areas 55 which can be of substantially identical radial height.

[0030] As yet another example, as schematically depicted in FIG. 10,each of the dark areas 61-65 can be of lighter shades of gray than thedark areas 55 which can be of substantially the same shade of gray, suchthat the dark areas 61-65 have greater reflectance (in a reflectivesystem) or transmissivity (in a transmissive system). Alternatively,each of the dark areas 61-65 can be of darker shades of gray than thedark areas 55 so as to have less reflectance (in a reflective system) ortransmissivity (in a transmissive system). Also, the dark areas 61-65can have a different pattern or patterns than dark areas 55, such thatthe dark areas 61-65 can have a greater reflectance (in a reflectivesystem) or transmissivity (in a transmissive system) than the dark areas55, or less reflectance (in a reflective system) or transmissivity (in atransmissive system) than the dark areas 55.

[0031] Effectively, the optical characteristics of each of the darkareas 61-65, 55 is configured to achieve a desired change in amplitudeof the quadrature output waveforms of the quadrature optical encodersensor 19 when the dark areas 61-65 are sensed. It should be appreciatedthat the various techniques for changing the optical characteristics ofthe dark areas can be employed individually or in combination.

[0032] Relative to the foregoing linear and circular optical tracks, thechange in optical characteristics of the dark areas 61-65 can be abruptor gradual over the span of the dark areas 61-65. For example, thewidths of the dark areas 61-65 can be substantially identical. Asanother example, the widths of the dark areas 61-65 can decrease andthen increase, whereby the dark area 63 is the narrowest. Similarly, thewidths of the dark areas 61-65 can increase and then decrease such thatthe dark area 63 is the widest of the dark areas 61-65.

[0033] By way of illustrative example, the widths of the dark areas 55can be about 50 percent of the pitch C, and the dark areas 61-65 candecrease to a width of about 30 percent of the pitch C. Also by way ofillustrative example, the optically different dark areas 61-65 cancomprise 74 bars arranged as follows, for example in a left to right orclockwise direction: 30 bars that decrease in width, 14 central barshaving a width of about 30 percent of the pitch C, and 30 bars thatincrease in width.

[0034] The invention has been described with reference to disclosedembodiments, and it will be appreciated that variations andmodifications can be affected within the spirit and scope of theinvention.

What is claimed is:
 1. An optical encoder comprising: an optical gratingfor modulating a beam of light; a sensor for sensing modulated lightprovided by the optical grating; the optical grating and the sensorbeing movable relative to each other; and the optical grating includinga plurality of contiguously adjacent first encoder bars and a pluralityof second encoder bars, wherein the contiguously adjacent first encoderbars and the second encoder bars are substantially uniformly spaced andwherein the first encoder bars are optically configured to change anamplitude of an output of the sensor.
 2. The optical encoder of claim 1wherein the second encoder bars are of substantially identical width. 3.The optical encoder of claim 1 wherein the contiguously adjacent firstencoder bars are wider than the second encoder bars.
 4. The opticalencoder of claim 1 wherein the contiguously adjacent first encoder barsare wider than the second encoder bars and are of gradually changingwidth.
 5. The optical encoder of claim 1 wherein the contiguouslyadjacent first encoder bars are narrower than the second encoder bars.6. The optical encoder of claim 1 wherein the contiguously adjacentfirst encoder bars are narrower than the second encoder bars and are ofgradually changing width.
 7. The optical encoder of claim 1 wherein thecontiguously adjacent first encoder bars are shorter than the secondencoder bars.
 8. The optical encoder of claim 1 wherein the contiguouslyadjacent first encoder bars are shorter than the second encoder bars andare of gradually changing height.
 9. The optical encoder of claim 1wherein the continguously adjacent first encoder bars are taller thanthe second encoder bars.
 10. The optical encoder of claim 1 wherein thecontiguously adjacent first encoder bars are taller than the secondencoder bars and are of gradually changing height.
 11. The opticalencoder of claim 1 wherein the second encoder bars are of substantiallyidentical darkness.
 12. The optical encoder of claim 1 wherein thecontiguously first encoder bars are lighter than the second encoderbars.
 13. The optical encoder of claim 1 wherein the contiguouslyadjacent first encoder bars are darker than the second encoder bars. 14.The optical encoder of claim 1 wherein the contiguously adjacent firstencoder bars are more transmissive than the second encoder bars.
 15. Theoptical encoder of claim 1 wherein the contiguously adjacent firstencoder bars are less transmissive than the second encoder bars.
 16. Theoptical encoder of claim 1 wherein the contiguously adjacent firstencoder bars and the second encoder bars include non-linear sides. 17.The optical encoder of claim 1 wherein the plurality of second encoderbars are disposed on both sides of the contiguously adjacent firstencoder bars.
 18. An optical encoder comprising: an optical grating formodulating a beam of light; a sensor for sensing modulated lightprovided by the optical grating; the optical grating and the sensorbeing movable relative to each other; and the optical grating includinga plurality of contiguously adjacent first encoder bars of respectivefirst encoder bar widths and a plurality of second encoder bars of asubstantially constant second encoder bar width, wherein thecontiguously adjacent first encoder bars and the second encoder barshave non-linear sides and are substantially uniformly spaced, andwherein each of the first encoder bar widths is different from thesubstantially constant second encoder bar width.
 19. The optical encoderof claim 18 wherein the first encoder bars are narrower than the secondencoder bars.
 20. The optical encoder of claim 18 wherein the first encoder bars are narrower than the second encoder bars and are ofgradually changing width.
 21. The optical encoder of claim 18 whereinthe first encoder bars are wider than the second encoder bars.
 22. Theoptical encoder of claim 18 wherein the first encoder bars are widerthan the second encoder bars and are of gradually changing width. 23.The optical encoder of claim 18 wherein the plurality of second encoderbars are disposed on both sides of the contiguously adjacent firstencoder bars.
 24. A position encoder comprising: an optical track forproviding a pattern of alternating light and dark areas, wherein thedark areas are substantially uniformly spaced and optically encoded todefine a predetermined position; and a quadrature sensor for detectingthe pattern of alternating light and dark areas.
 25. A position encodercomprising: means for providing a pattern of alternating light and darkareas; and means for detecting movement of the pattern to determine aposition of the pattern.
 26. An optical grating comprising: a pluralityof contiguously adjacent first encoder bars; a plurality of secondencoder bars; and wherein the contiguously adjacent first encoder barsand the second encoder bars are substantially uniformly spaced andwherein the first encoder bars are optically different from the secondencoder bars.
 27. The optical grating of claim 26 wherein the secondencoder bars are of substantially identical width.
 28. The opticalgrating of claim 26 wherein the contiguously adjacent first encoder barsare narrower than the second encoder bars.
 29. The optical grating ofclaim 26 wherein the contiguously adjacent first encoder bars arenarrower than the second encoder bars and are of gradually changingwidth.
 30. The optical grating of claim 26 wherein the contiguouslyadjacent first encoder bars are wider than the second encoder bars. 31.The optical grating of claim 26 wherein the contiguously adjacent firstencoder bars are wider than the second encoder bars and are of graduallychanging width.
 32. The optical grating of claim 26 wherein thecontiguously adjacent first encoder bars are shorter than the secondencoder bars.
 33. The optical grating of claim 26 wherein thecontiguously adjacent first encoder bars are shorter than the secondencoder bars and are of gradually changing height.
 34. The opticalgrating of claim 26 wherein the continguously adjacent first encoderbars are taller than the second encoder bars.
 35. The optical grating ofclaim 26 wherein the contiguously adjacent first encoder bars are tallerthan the second encoder bars and are of gradually changing height. 36.The optical grating of claim 26 wherein the second encoder bars are ofsubstantially identical darkness.
 37. The optical grating of claim 26wherein the contiguously first encoder bars are lighter than the secondencoder bars.
 38. The optical grating of claim 26 wherein thecontiguously adjacent first encoder bars are darker than the secondencoder bars.
 39. The optical grating of claim 26 wherein thecontiguously adjacent first encoder bars are more transmissive than thesecond encoder bars.
 40. The optical grating of claim 26 wherein thecontiguously adjacent first encoder bars are less transmissive than thesecond encoder bars.
 41. The optical grating of claim 26 wherein thecontiguously adjacent first encoder bars and the second encoder barsinclude the non-linear sides.
 42. The optical grating of claim 26wherein the plurality of second encoder bars are disposed on both sidesof the contiguously adjacent first encoder bars.
 43. An optical gratingcomprising: a plurality of contiguously adjacent first encoder barshaving respective first encoder bar widths; a plurality of secondencoder bars having a substantially constant second encoder bar width;and wherein the contiguously adjacent first encoder bars and the secondencoder bars have non-linear sides and are substantially uniformlyspaced, and wherein the first encoder bar widths are different from thesecond encoder bar width.
 44. The optical grating of claim 43 whereinthe first encoder bars are narrower than the second encoder bars. 45.The optical grating of claim 43 wherein the first en coder bars arenarrower than the second encoder bars and are of gradually changingwidth.
 46. The optical grating of claim 43 wherein the first encoderbars are wider than the second encoder bars.
 47. The optical grating ofclaim 43 wherein the first encoder bars are wider than the secondencoder bars and are of gradually changing width.
 48. The opticalgrating of claim 43 wherein the plurality of second encoder bars aredisposed on both sides of the contiguously adjacent first encoder bars.49. An optical grating comprising: a first encoder bar; a plurality ofsecond encoder bars; and wherein the contiguously adjacent first encoderbar and the second encoder bars are substantially uniformly spaced andwherein the first encoder bar is optically different from the secondencoder bars.
 50. The optical grating of claim 49 wherein the pluralityof second encoder bars are of substantially identical width.
 51. Theoptical grating of claim 49 wherein the first encoder bar is narrowerthan each of the plurality of second encoder bars.
 52. The opticalgrating of claim 49 wherein the first encoder bar is wider than each ofthe plurality of second encoder bars.
 53. The optical grating of claim49 wherein the first encoder bar is shorter than each of the pluralityof second encoder bars.
 54. The optical grating of claim 49 wherein thefirst encoder bar is taller than each of the plurality of second encoderbars.
 55. The optical grating of claim 49 wherein the plurality ofsecond encoder bars are of substantially identical darkness.
 56. Theoptical grating of claim 49 wherein the first encoder bar is lighterthan each of the plurality of second encoder bars.
 57. The opticalgrating of claim 49 wherein the first encoder bar is darker than each ofthe plurality of second encoder bars.
 58. The optical grating of claim49 wherein the first encoder bar is more transmissive than each of theplurality of second encoder bars.
 59. The optical grating of claim 49wherein the first encoder bar is less transmissive than each of theplurality of second encoder bars.
 60. The optical grating of claim 49wherein the first encoder bar and the plurality of second encoder barsinclude non-linear sides.
 61. The optical grating of claim 49 whereinthe plurality of second encoder bars are disposed on both sides of thefirst encoder bar.